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CHEMISTRY A LEVEL > CHAPTER 8 - REACTIVITY TRENDS > Flashcards

CHAPTER 8 - REACTIVITY TRENDS Flashcards

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1
Q

Why are group 2 elements known as reducing agents

A

They reduce other species

They are oxidised

eg. Ca —> Ca2+ + 2e-

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2
Q

What is formed when a redox reaction occurs between a metal and oxygen

A

Metal Hydroxide

eg. 2Mg + O2 –> 2MgO

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3
Q

What is formed when a redox reaction occurs between a metal and water

A

Metal Hydroxide + Hydrogen

eg. Sr + 2H2O –> Sr(OH)2 + H2

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4
Q

What is formed when a redox reaction occurs between a dilute acid and metal

A

Salt and Hydrogen

eg. Mg + 2HCl –> MgCl2 + H2

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5
Q

What are the solubility of Barium, Calcium, Magnesium and Strontium Hydroxides

A

Ba(OH)2 - Most soluble
Sr(OH)2
Ca(OH)2
Mg(OH)2 - Least soluble

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6
Q

Describe an experiment to show the trends in solubility of metal hydroxides

A

Add a spatula of each group 2 oxide to water in a test tube

Shake the mixture. On this scale, there is insufficient water to dissolve all of the metal hydroxide that forms. You will have a saturated solution of each metal hydroxide with some white solid undissolved at the bottom of the test-tube

Measure pH of each solution. The alkalinity will be sen to increase down the group

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7
Q

What are group 2 compounds used for in agriculture

A

Calcium Hydroxide added to fields as lime by farmers to increase pH of soils

Ca(OH)2 + 2H+ –> Ca2+ + 2H2O

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8
Q

What are group 2 compounds used for in medicine

A

Antacids to treat indigestion eg. Milk of magnesia or Calcium carbonates to neutralise stomach acids

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9
Q

Explain why group 2 elements are reducing agents

A

Group 2 metals add electrons to other species

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10
Q

Explain why the group 2 elements become more reactive down the group

A

Down group 2, the total energy from 1st and 2nd ionisation energies decreases because of increased atomic radius and increased shielding

It therefore becomes easier to remove the electrons and the reactivity increases

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11
Q

State and explain the trend in alkalinity of the solution formed when group 2 oxides are added to water

A

Group 2 oxides react with water forming the metal hydroxide.

Hydroxide ions in solution cause alkalinity.

Down group 2, the solubility of the metal hydroxide increases, increasing the pH and alkalinity

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12
Q

What is the name of Group 17 (7)

A

The halogens

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13
Q

Where to halogens occur

A

Stable halide ions, dissolved in sea water or combined with sodium or potassium deposits in salt mines

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14
Q

What colours and states do halogens form at RTP

A

Fluorine - Yellow Gas
Chlorine - Green Gas
Bromine - Red-Brown liquid
Iodine - Grey-black solid

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15
Q

Why are halogens known as oxidising agents

A

They cause oxidation in other species

causing themselves to be reduced

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16
Q

What is the trend of reactivity down the halogen group

A

It Decreases

17
Q

What colours do Chlorine, bromine and iodine form in water

A

Cl - Pale green
Br - Orange
I - Brown

18
Q

What colours do Chlorine, Bromine and Iodine form in cyclohexane

A

Cl - Pale green
Br - Orange
I - Violet

19
Q

Why do halogens dissolve more readily into cyclohexane than water

A

Halogens and cyclohexanes are non-polar

Water is polar

20
Q

What is the Displacement trend in halogens

A

Cl displaces Br and I
Br displaces I
I displaces nothing
(pg 113)

21
Q

What is the displacement reaction of chlorine and sodium bromide

A

Cl2 + 2NaBr –> 2NaCl + Br2

22
Q

What is a disproportionation reaction

A

A redox reaction in which the same element is both oxidised and reduced

23
Q

What is chlorine used for

A

Water purification killing harmful bacteria

Cl2 + H2O –> HClO + HCl

24
Q

How can a disproportionate reaction be seen

A

Adding indicator into a solution of chlorine and water

Turns red in the presence of HCl and disappears after the bleaching action of HClO (Chloric acid)

25
Q

What is formed in the reaction of Cold, dilute NaOH (aq)

A

NaClO, NaCl and H2O

Disproportionation reaction

26
Q

What is the test for Halide ions

A

Adding Aqueous silver ions, eg. Silver nitrate

27
Q

State and explain the trend in boiling points of the halogens fluorine to iodine

A

Boiling point increases due to increasing electrons downgrade

This increases the strength of the London forces are more energy needed to break the intermolecular forces

28
Q

What is the test for carbonate ions

A

Add Dilute nitric acid - effervescences

OR

Lime water test (Ca(OH)2) - goes cloudy

29
Q

What is the test for Sulfate ions

A

Add Barium Chloride or barium nitrate

Will form BaSO4 - white ppt

SBC

30
Q

What is the test for Halides

A

Add aqueous AgNO3 - forms 3 ppts of different colours, AgX

Add Aqueous NH3 - to test solubility

Cl - White ppt, Soluble Dilute NH3
Br - Cream ppt, soluble conc. NH3
I - Yellow ppt, Insoluble conc. NH3

HAgA

31
Q

What is the correct order for Anion testing and why

A

1- Carbonate - no other test produces bubbles after this

2- Sulfate - forms white ppt, important to make sure it isn’t a carbonate which would look like a positive test if done after this due to the colour

3- Halide test, silver carbonate and silver sulfate will form precipitates insoluble in water

32
Q

What is the test for ammonium

A

Add aqueous NaOH

Ammonia Gas will be produced - little bubbles formed as it is soluble with water

Mixture is warmed by reaction

Smell of ammonia and alkaline ammonia gas will turn damp pH paper blue

33
Q

How could you distinguish between NaCl, NaBr and NaI by a simple test?

A

Add AgNO3 to aqueous solutions of each.

NaCl forms white ppt, dissolves In dilute NH3
NaBr forms cream ppt which dissolves in concentrated NH3
NaI forms yellow ppt, insoluble in conc NH3

34
Q

Explain why it is important to carry out the carbonate test before carrying out the sulfate test on an unknown chemical

A

Dilute Nitric acid with carbonate ions, and no precipitate of barium carbonate will then form

35
Q

Explain why if you are testing a mixture, it is important to use dilute nitric acid rather than sulphuric or hydrochloric for the carbonate test

A

If sulphuric acid is used, sulphate ions are added and will show up in the sulphate test

If hydrochloric acid is used, chloride ions are added, and will sharp in the halide test.

36
Q

What is the purpose of a Barium meal

A

Coats inner lining of gut which will show up on x-ray - as it is insoluble (BaSO4 with water is taken)

Barium is usually toxic, but it doesn’t interact with the body due to BaSO4 being so insoluble

CHEMISTRY A LEVEL (14 decks)

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